To cross a stream, road or valley (where by the hold off brought on by a flight of locks at both aspect could well be unacceptable) the valley might be spanned by a navigable aqueduct – a well-known illustration in Wales is the Pontcysyllte Aqueduct (now a UNESCO Environment https://ursofofo55543.therainblog.com/35925719/5-easy-facts-about-musica-infantil-described